maillist inclusion category: bugfix bugzilla: 189317, https://gitee.com/openeuler/kernel/issues/I76JSK CVE: NA

Reference: https://lore.kernel.org/all/20231216115559.3823359-1-leo.lilong@huawei.com/

--------------------------------

While fsstress + drop cache test, we get following warning:

------------[ cut here ]------------ WARNING: CPU: 2 PID: 1003 at fs/iomap/buffered-io.c:1182 iomap_file_buffered_write_punch_delalloc+0x691/0x730 Modules linked in: CPU: 2 PID: 1003 Comm: fsstress Not tainted 6.7.0-rc5-06945-g3ba9b31d6bf3-dirty #256 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20190727_073836-buildvm-ppc64le-16.ppc.fedoraproject.org-3.fc31 04/01/2014 RIP: 0010:iomap_file_buffered_write_punch_delalloc+0x691/0x730 Code: d1 0b 01 0f 0b 48 83 05 14 a2 d1 0b 01 48 89 05 35 a1 d1 0b 49 39 ec 0f 8c 09 fb ff ff e9 b6 fd ff ff 48 83 05 df a1 d1 0b 01 <0f> 0b 48 83 05 dd a1 d1 0b 01 48 39 6c 24 10 7c c0 48 89 05 07 a1 RSP: 0018:ffffc900005b7b08 EFLAGS: 00010202 RAX: 0000000000000001 RBX: ffff888102363d40 RCX: 0000000000000001 RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff888108080000 RBP: 0000000000050000 R08: ffff888108084eb8 R09: ffff888108084eb8 R10: 000000000000005c R11: 0000000000000059 R12: 0000000000050000 R13: ffffffff8c978ef0 R14: 0000000000050000 R15: 000000000005a000 FS: 00007efc04c63b40(0000) GS:ffff88813bd00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007efc0375c000 CR3: 0000000105a4d000 CR4: 00000000000006f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <TASK> xfs_buffered_write_iomap_end+0x40/0xb0 iomap_iter+0x8e/0x5f0 iomap_file_buffered_write+0xa4/0x460 xfs_file_buffered_write+0x156/0x3d0 xfs_file_write_iter+0xb2/0x1c0 do_iter_readv_writev+0x19b/0x1f0 vfs_writev+0x114/0x4f0 do_writev+0x7f/0x1c0 __x64_sys_writev+0x24/0x30 do_syscall_64+0x3f/0xe0 entry_SYSCALL_64_after_hwframe+0x62/0x6a RIP: 0033:0x7efc03b06610 Code: 73 01 c3 48 8b 0d 78 88 2c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00 83 3d d9 e0 2c 00 00 75 10 b8 14 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 5e 8e 01 00 48 89 04 24 RSP: 002b:00007ffdf8f426d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000014 RAX: ffffffffffffffda RBX: 000000000000007a RCX: 00007efc03b06610 RDX: 00000000000002c4 RSI: 00000000012f5580 RDI: 0000000000000003 RBP: 0000000000000003 R08: 00000000012f53a0 R09: 0000000000000077 R10: 000000000000007c R11: 0000000000000246 R12: 00000000000002c4 R13: 00000000012dba50 R14: 00000000012f5580 R15: 0000000000000094

The warning occurred in the following code of iomap_write_delalloc_release(). After analyzing vmcore, I found that the reason for the warning is that data_end was equal to start_byte.

WARN_ON_ONCE(data_end <= start_byte);

If some delay is added between seeking for data and seeking for hole in iomap_write_delalloc_release(), the problem can be reproduced quickly. The root cause of the problem is that clean data page was dropped between two seeking in the page cache. As a result, data_end may be equal to start_byte.

buffered write drop cache --------------------------- --------------------------- xfs_buffered_write_iomap_end iomap_file_buffered_write_punch_delalloc iomap_write_delalloc_release start_byte = mapping_seek_hole_data(SEEK_DATA)

drop_pagecache_sb invalidate_mapping_pages mapping_try_invalidate mapping_evict_folio remove_mapping

data_end = mapping_seek_hole_data(SEEK_HOLE) WARN_ON_ONCE(data_end <= start_byte)

In my investigation, I found that clean data pages was alloced and added to page cache when reading the file's hole. After that, while buffered write and goes into delalloc release, we seek for data, it will find the start offset of the clean data pages. If the clean data pages was dropped, when we seek for hole, it will find the same offset as the previous seek.

During delalloc release, we punch out all the delalloc blocks in the range given except for those that have dirty data still pending in the page cache. If the start_byte is equal to data_end after seeking data and hole, it will be returned directly in the delalloc scan, and we can continue to find the next data, and perform delalloc scan. It does not affect the range of delalloc block that need to be punched out.

Therefore, if start_byte equal to data_end, just let it seek for data again in the loop.

Fixes: f43dc4dc3eff ("iomap: buffered write failure should not truncate the page cache") Signed-off-by: Long Li leo.lilong@huawei.com --- fs/iomap/buffered-io.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c index dbd56c36ce2b..049b3a6f9b08 100644 --- a/fs/iomap/buffered-io.c +++ b/fs/iomap/buffered-io.c @@ -1227,7 +1227,17 @@ static int iomap_write_delalloc_release(struct inode *inode, error = data_end; goto out_unlock; } - WARN_ON_ONCE(data_end <= start_byte); + + /* + * Seek for data/hole in the page cache can race with drop + * cache, if data page was dropped between seek for data and + * hole, data_end may be equal to start_byte, just let it keep + * seeking. + */ + if (data_end == start_byte) + continue; + + WARN_ON_ONCE(data_end < start_byte); WARN_ON_ONCE(data_end > scan_end_byte);

error = iomap_write_delalloc_scan(inode, &punch_start_byte,